Ion liquids derived from lewis acid based on titanium, niobium, tantalum, tin or antimony, and uses thereof

ABSTRACT

The ionic liquids according to the invention result from the reaction of a halogenated or oxyhalogenated Lewis acid based on titanium, niobium, tantalum, tin or antimony with an organic salt of formula X + A −  in which A −  is a halide anion and X +  a quaternary ammonium, quaternary phosphonium or ternary sulphonium cation.  
     These liquids can be used in particular in the liquid-phase fluorination by HF of saturated or unsaturated compounds exhibiting C—Cl bonds.

[0001] The present invention relates to ionic liquids and has more particularly as subject-matter ionic liquids based on titanium, niobium, tantalum, tin or antimony.

[0002] The ionic liquids as considered in the present patent application are nonaqueous salts with an ionic nature which are liquid at moderate temperatures and which result from the reaction between an organic salt and an inorganic compound, A certain number of ionic liquids are already known. Thus, in J. Am. Chem. Soc. 101, 2, 323-327 (1979), Osteryoung et al. have demonstrated that the mixture of butylpyridinium chloride (A) and of aluminium chloride AlCl₃ (B) is liquid at 40° C. aver a wide range of compositions (A/B molar ratio ranging from 1/0.75 to 1/2). In Inorg. Chem. 21, 1263-1264, Wilkes et al. have shown that the compounds resulting from the reaction between AlCl₃ and a dialkylimidazolium chloride, such as 1-butyl-3-methylimidazolium chloride, are liquid at room temperature, also for the same range of compositions described above. In this example of an ionic liquid, the dialkylimidazolium constitutes the cation and AlCl₄ the anion. Other anions, such as nitrate, acetate or tetrafluoroborate anions, can be used (see the publication Wo 9618459).

[0003] Due to their wide electrochemical window, ionic liquids can be used as battery electrolytes. They are also particularly useful in catalysis, as they are excellent solvents for organometallic compounds. Thus, for example, Patent Applications FR 2,626,572 and WO 9521806 disclose the use of the above-mentioned compounds based on chloroaluminate in the alkylation, in two-phase catalysis, of aromatic or isoparaffin compounds.

[0004] A subject-matter of the invention is now ionic liquids derived from Lewis acids based on titanium, niobium, tantalum, tin or antimony. These ionic liquids find applications in catalysis and can also have properties of solvating organometallic compounds capable of being used in two-phase catalysis.

[0005] The ionic liquids according to the invention, which are aprotic nonaqueous ionic compounds which are liquid over a range of moderate temperatures (preferably below 100° C.) at atmospheric pressure, are obtained by reaction of a halogenated or oxyhalogenated Lewis acid based on titanium, niobium, tantalum, tin or antimony with a salt of general formula X⁺A⁻ in which A⁻ denotes a halide (bromide, iodide and, preferably, chloride or fluoride) anion and X′ a quaternary ammonium, quaternary phosphonium or ternary sulphonium cation.

[0006] The halogenated Lewis acid based on titanium, niobium, tantalum, tin or antimony can be a chlorinated, brominated, fluorinated or mixed derivative, for example a chlorofluorinated acid. Mention may more particularly be made of the chlorides, fluorides or chlorofluorides with the following formulae:

[0007] TiCl_(x)F_(y) with x+y=4 and 0≦x≦4

[0008] TaCl_(x)F_(y) with x+y=5 and 0≦x≦4

[0009] NbCl_(x)F_(y) with x+y=5 and 0≦x≦5

[0010] SnCl_(x)F_(y) with x+y=4 and 1≦x≦4

[0011] SbCl_(x)F_(y) with x+y=5 and 0≦x≦5

[0012] Mention may be made, as examples of such compounds, of the following compounds: TiCl₄, TiF₄, TaF₅, NbCl₅, NbF₅, SnCl₄, SnF₄, SbCl₅, SbCl₄F, SbCl₃F₂, SbCl₂F₃, SbClF₄ and SbFs. Use is preferably made, among these compounds, of the following: TiCl₄, TiF₄, TaF₅, NbF₅, SnCl₄, SbFCl₄, SbF₂Cl₃, SbF₃Cl₂, SbF₄Cl and SbF₅. Preference is even more particularly given to TiCl4, TaF₅, SbFCl₄, SbF₂Cl₃, SbF₃Cl₂, SbF₄Cl and SbF₅.

[0013] Mention may be made, as examples of oxyhalogenated Lewis acids which can be used according to the invention, of TiOCl₂, TiOF₂, SnOCl₂, SnOF₂ and SbOCl_(x)F_(y) (x+y=3).

[0014] In the salt X′A⁻, the cation X⁺ can correspond to one of the following general formulae:

[0015] R¹R²R³R⁴N⁺

[0016] R¹R²R³R⁴P⁺

[0017] R¹R²R³S⁺

[0018] in which the symbols R¹ to R⁴, which are identical or different, each denote a saturated or unsaturated, cyclic or noncyclic or aromatic, hydrocarbyl, chlorohydrocarbyl, fluorohydrocarbyl, chlorofluorohydrocarbyl or fluorocarbyl group having from 1 to 10 carbon atoms, it being possible for one or more of these groups also to comprise one or more heteroatoms, such as N, P, S or O.

[0019] The ammonium, phosphonium or sulphonium cation X⁺ can also form part of a saturated or unsaturated or aromatic heterocycle having from 1 to 3 nitrogen, phosphorous or sulphur atoms and can correspond to one or other of the following general formulae:

[0020] in which R¹ and R² are as defined above.

[0021] It would not be departing from the scope of the present invention to use a salt comprising 2 or 3 ammonium, phosphonium or sulphonium sites in its formula, Mention may be made, as examples of salts X⁺A⁻, of tetraalkylammonium chlorides and fluorides, tetraalkylphosphonium chlorides and fluorides and trialkylsulphonium chlorides and fluorides, and alkylpyridinium chlorides and fluorides, dialkylimidazolium chlorides, fluorides and bromides and trialkylimidazolium chlorides and fluorides. Trimethylsulphonium chloride or fluoride, N-ethylpyridinium chloride or fluoride, N-butylpyridinium chloride or fluoride, 1-ethyl-3-methylimidazolium chloride or fluoride and 1-butyl-3-methylimidazolium chloride or fluoride are more particularly valued.

[0022] The ionic liquids according to the invention can be prepared in a way known per se by appropriately mixing the halogenated or oxyhalogenated Lewis acid and the organic salt X⁺A⁻ in a molar ratio which can range from 0.5/1 to 3.5/1, preferably from 1/1 to 2.5/1 and more preferably from 1/1 to 2/1. A molar ratio rigorously greater than 1/1 is particularly recommended if it is desired to obtain an acidic ionic liquid.

[0023] The mixture can be prepared in a reactor of autoclave type, optionally cooled in order to limit the exothermicity of the reaction. It is also possible to control this exothermicity by gradually adding one of the reactants to the other.

[0024] When the Lewis acid/organic salt molar ratio is greater than 1/1, it can prove to be useful to heat the reaction medium until the solid has completely dissolved.

[0025] As the reactants and the ionic liquid obtained are generally hygroscopic, it is recommended to carry out the synthesis with air and water excluded while using, to this end, the means known to a person skilled in the art.

[0026] The ionic liquids according to the invention can be used in all the applications known for compounds of this type. When the Lewis acid/organic salt molar ratio is less than or equal to 1/1, these liquids can be used for their solvating properties (organic synthesis, solvents for organometallic complexes).

[0027] When the Lewis acid/organic salt molar ratio is rigorously greater than 1/1, the ionic liquids according to the invention have acidic properties which are advantageous in any catalysis requiring the use of an acid catalyst, for example Friedel-Crafts catalysis and fluorination catalysis.

[0028] The ionic liquids according to the invention find a particularly advantageous use in the liquid-phase fluorination by HF of saturated or unsaturated compounds exhibiting C—Cl bonds, such as, for example, CHCl═CH₂, CCl₂═CCl₂, CH₂═CCl₂, CClH═CCl₂, CH₂Cl₂, CH₂ClF, CCl₃—CH₃, CCl₂H—CCl₂H, CCl₃—CH₂Cl, CCl₃—CHCl₂, CF₃—CH₂Cl, CCl₃—CH₂—CHCl₂, CF₃—CH—CHCl or CCl₃—CH₂—CCl₂—CH₃.

[0029] A liquid-phase fluorination process using an ionic liquid according to the invention as catalyst can be carried out batchwise. The equipment used is then an autoclave, into which the reactants and the catalyst are introduced before the beginning of the reaction, the pressure in the autoclave varying with the progress of the reaction. The molar amount of HF to the molar amount of starting material is between 2 and 50 and preferably between 10 and 30. The duration of the reaction required, which depends on the amount of the reactants involved at the start and on the various operating parameters, can be easily known experimentally.

[0030] The fluorination can also be carried out according to a semi-continuous form in equipment composed of an autoclave, surmounted by a simple condenser or by a return column with a reflux condenser, and of a pressure-regulating valve, the pressure being chosen so as to keep the reaction medium in the liquid state. As above, the reactants and the catalyst are introduced beforehand into the reactor but the reaction products with low boiling points (fluorinated products) and the hydrogen chloride (HCl) co-product are continuously extracted during the reaction while the compounds with higher boiling points, such as the starting materials, the intermediate products and the HF, largely flow back in liquid form into the reaction medium by virtue of the condenser (or return column) placed above the reactor.

[0031] In accordance with a third embodiment, the fluorination can be carried out continuously in the same equipment as semi-continuously but at least one of the reactants (HF or the starting material) is introduced continuously. In the context of an industrial process, it is preferable to feed the two reactants conjointly. The reaction products are extracted continuously during the reaction, the unconverted reactants flowing back into the reactor. The molar amount of fed HF to the molar amount of fed starting material is at least equal to 2.

[0032] The amount of catalyst depends on the operating conditions and on the reaction medium (in the case of a continuous process) but also on the intrinsic activity of the catalyst. This amount is between 0.5 and 90% (molar) of the reaction medium.

[0033] The temperature at which the fluorination reaction is carried out (under batchwise and continuous conditions) is generally between 30 and 180° C., preferably between 80 and 130° C.

[0034] The pressure at which the reaction is carried out in the semi-continuous or continuous forms is chosen so as to keep the reaction medium in the liquid phase. It is generally between 5 and 50 bar and preferably between 10 and 40 bar; under continuous conditions, if HF constitutes the reaction medium, the operating pressure chosen is generally the saturated vapour pressure of HF at the desired reaction temperature. The temperature of the condenser is determined upon according to the amount and the nature of the products capable of being discharged during the reaction. It is generally between −50 and 150° C. and preferably between 0 and 100° C.

[0035] The material of the fluorination reactor must make it possible to operate under the pressure and temperature conditions defined above. It must also withstand the corrosion generated by the hydrogen fluoride. Thus, stainless steel or alloys of Monel, Inconel or Hastelloy type are particularly indicated.

[0036] The following examples illustrate the invention without limiting it.

EXAMPLE 1

[0037] 7.3 g of 1-ethyl-3-methylimidazolium chloride (emim-Cl) were introduced into a Schlenk tube while flushing with argon and then the tube was immersed in ice. Antimony chlorofluoride SbF₃Fl₂ was then gradually introduced with stirring. The reaction is exothermic but the ice made it possible to keep the temperature of the tube at approximately 10° C. After having introduced 12.6 g of SbF₃Cl₂, corresponding to an SbF₃Cl₂/emim-Cl molar ratio of 1, the Schlenk tube was heated to approximately 40° C. in order to completely liquefy the ionic liquid formed. Addition of SbF₃Cl₂ was then continued at room temperature until the total mass introduced was 25.3 g, corresponding to an SbF₃Cl₂/emim-Cl molar ratio of 2.

[0038] After stirring for 18 hours at room temperature, 32.6 g of an ionic liquid were obtained. This compound was analysed by infrared and raman spectroscopy and exhibits the following main characteristics:

[0039] band at 1600 cm⁻¹ (attributable to the C═N bond)

[0040] band between 550 and 600 cm⁻¹

[0041] Raman

[0042] band at 370 cm⁻¹

[0043] band at 174 cm⁻¹

EXAMPLE 2

[0044] Example 1 was repeated but replacing antimony chlorofluoride with 27.9 g of tantalum pentafluoride (TaF₅).

EXAMPLES 3 to 14

[0045] Other examples of ionic liquids according to the invention obtained in the same way as in Examples 1 and 2 are summarized in the following table. They are all liquid at room temperature, except that of Example 10, which is liquid from 100° C. Lewis Characteristic acid/emim-Cl (% by mass of Example Lewis acid molar ratio metal analysed) 3 TiCl₄ 1/1 14 4 TiCl₄ 2/1 18 5 TiF₄ 1/1 17 6 TaF₅ 1/1 43 7 SbF₃Cl₂ 2/1 37 8 SbF₄Cl 1/1 31 9 SbF₄Cl 2/1 39 10 NbCl₅ 1/1 22 11 NbF₅ 1/1 29 12 SnCl₄ 1/1 29 13 SbF₅ 1/1 33 14 SbF₅ 2/1 43

EXAMPLE 15

[0046] 30.6 g of the ionic liquid of Example 9, 21.5 g of methylene chloride (F30) and 20.8 g of HF were successively charged to a 0.150 litre autoclave made of 316L stainless steel. The autoclave was then immersed in an oil bath at 130° C., the temperature of the condenser being kept at 15-20° C. and the regulating pressure being set at 10 bar absolute. At this pressure, the temperature of the reaction medium was approximately 100° C.

[0047] During the reaction, the volatile reaction products were discharged continuously and passed into a water bubbler and then into a dryer before being collected in a stainless steel trap cooled with liquid nitrogen. After reacting for 290 minutes, the autoclave was cooled with circulating water. After returning to room temperature, the autoclave was degassed and the reaction products were washed, dried and trapped as above.

[0048] Analysis of the gas phase and of the liquid phase from the various traps showed that 84% of the starting F30 was converted, 69% of which into difluoromethane and 31% of which into chlorofluoromethane (mol %). 

1. Ionic liquid composed of the reaction product of a halogenated or oxyhalogenated Lewis acid based on titanium, niobium, tantalum, tin or antimony with an organic salt of general formula X⁺A⁻ in which A⁻ is a halide anion and X⁺ a quaternary ammonium, quaternary phosphonium or ternary sulphonium cation.
 2. Ionic liquid according to claim 1, in which the Lewis acid/organic salt molar ratio is between 0.5/1 and 3.5/1, preferably between 1/1 and 2.5/1 and more particularly between 1/1 and 2/1.
 3. Ionic liquid according to claim 1 or 2, in which the Lewis acid is a titanium, niobium, tantalum, tin or antimony chloride, fluoride or chlorofluoride.
 4. Ionic liquid according to claim 3, in which the Lewis acid is chosen from TiCl₄, TaF₅, SbFCl₄, SbF₂Cl₃, SbF₃Cl₂, SbF₄Cl and SbF₅.
 5. Ionic liquid according to one of claims 1 to 4, in which the organic salt X⁺A⁻ is a chloride or a fluoride, the cation X⁺ corresponding to one of the following general formulae: R¹R²R³R⁴N⁺ R¹R²R³R⁴P⁺ R¹R²R³S⁺ in which the symbols R¹ to R⁴, which are identical or different, each denote a saturated or unsaturated, cyclic or noncyclic or aromatic, hydrocarbyl, chlorohydrocarbyl, fluorohydrocarbyl, chlorofluorohydrocarbyl or fluorocarbyl group having from 1 to 10 carbon atoms, it being possible for one or more of these groups also to comprise one or more heteroatoms.
 6. Ionic liquid according to one of claims 1 to 4, in which the organic salt X⁺A⁻ is a chloride or a fluoride, the cation X⁺ forming part of a saturated or unsaturated or aromatic heterocycle having from 1 to 3 nitrogen, phosphorus or sulphur atoms and corresponding to one or other of the following general formulae:

in which R¹ and R² are as defined in claim
 5. 7. Ionic liquid according to claim 5 or 6, in which the cation X⁺ is a tetraalkylammonium, tetraalkylphosphonium, trialkylsulphonium, alkylpyridinium, dialkylimidazolium or trialkylimidazolium cation, preferably a trimethylsulphonium, N-ethylpyridinium, N-butylpyridinium, 1-ethyl-3-methylimidazolium or 1-butyl-3-methylimidazolium cation.
 8. Process for the liquid-phase fluorination by HF of a saturated or unsaturated compound exhibiting C—Cl bonds, characterized in that an ionic liquid according to one of claims 1 to 7 is used as catalyst. 